Labour will today attempt to stave off a bid to veto its bill to extend paid parental leave to six months.

The legislation is before Parliament again today and has enough support to pass.

However, National plans to extend the paid leave from 14 to 18 weeks - and Finance Minister Bill English has said he'll exercise a seldom-used financial veto on Labour's bill.

MP Sue Moroney is guiding the bill through the House, and she is to propose an amendment which means the extra leave won't kick in until next year. She says National then won't need to axe the bill because the current Government is not responsible for next year's Budget.

"There is no grounds for a financial veto now that I have put an amendment forward that doesn't impact on the financial year that this Government is responsible for," she explained.

"What my amendment does is pushes it out so that it would bring in 22 weeks' paid parental leave on July 1. The final extra four weeks, to bring it up to 26 weeks, [will come in] on July 1, 2017."

Since the departure of sole ACT MP John Banks earlier this month, Moroney has support from all parties bar National.

However, progress of the bill has been tortuous since it was first drawn from the members' ballot in 2012. Last month it failed at the second reading in shambolic scenes after a paperwork gaffe by the Maori Party. The error was corrected the following day and the bill will enter committee stages this afternoon.

After discussions with parliamentary officials, Labour believes National will have to exercise the veto before its final reading, scheduled for July 23.

"There has never been a financial veto put before an entire bill," Moroney said. "It's a first and the Clerk's Office is not 100 per cent sure about what happens next. They believe the Government would have to put the veto on before the final reading. Once it is read a third time, that's a done deal. It's then passed into law."

Also up for debate today are a local bill and legislation outlawing hand-held lasers. National has not indicated it will delay proceedings by filibustering.

Moroney's parents, Mary and Denny, are travelling to Wellington for today's debate - also their 59th wedding anniversary.

In May's Budget, English announced $171.8 million over four years to extend leave from 14 weeks to 18. From April, leave will be extended to 16 weeks, and then to 18 in April 2016. He was unavailable for comment last night.